The steel wheels shown are off of a K series truck. They do not fit the front of the C series as they are a different offset and rub on the control arms. I do believe that they will fit on the rear without any problems.
Years ago I had the same thing happen to me on an 85 S10 with the 700r4 in it. When I tore it down, the spines on the clutch plates of the forward clutch had worn down enough that when a load was placed on them to start moving again, they sheared off. When your trans was rebuilt previously...